This invention relates to movie projectors and, more particularly, to lighting sources for projecting images and releasing sound from a reel of film in a theater.
Successful motion picture projection depends on a concentrated light source that can be conveniently imaged on a projector aperture at the film plane.
Early movie theaters were small rooms with dimly lit screens because the candlepower of the "projection light source" was too small to allow for crisp, long-range projection. Even during the heyday of silent films, theaters operated in almost complete darkness, with dim flickering images being projected onto the screen.
Prior to expanding theaters to accommodate the thousands of patrons that theater owners envisioned, better sources of light were needed for projecting the film image onto the screen. Small theaters require less candlepower to project a crisp image. However, as taught in most basic physics courses, light weakens or diffuses in inverse proportion to the square of the distance it travels. Thus, if a theater were to be doubled, for example, the candlepower had to be quadrupled to produce the same quality picture.
Eventually, low and then higher intensity carbon arc lamps were introduced to provide better light. Then, came a primary breakthrough in around 1951: the invention of the xenon arc lamp. This new high-intensity light produced about 40-80 times the amount of light projected on the screens of the first theaters.
Because the xenon arc is very concentrated, crisper images could be projected over longer distances, and theaters could be enlarged. Consequently, along with its later improvements, the xenon arc lamphouse is the preferred light source now used in modern cinemas.
While the xenon lamphouse has its advantages, it also has its drawbacks. Due to its high concentration of light, it produces an extreme amount of infrared radiation that can be easily absorbed by the film near it.
When black-and-white film overheats, it becomes soft and its projected images begin to "flutter". Adjusting the projector's focus lens will not correct the situation. If the radiant energy is increased even further, blistering will occur. At this point, the film is useless for further projection.
Color prints are not as susceptible to heat transfer as their black-and-white counterparts, since they are made of relatively transparent dyes, while the black-and-whites are made of more radiant-absorbing silver fragments. Nonetheless, color prints suffer many of the same problems, only at higher temperatures.
To obviate this problem of heat transfer, special heat shields and lenses are used in the projector and cooling ducts are attached to the lamphouse. These special shields and lenses are expensive; further, the operating costs of the cooling ducts, namely, electricity and maintenance, are often extremely high.
Similar heating problems occur with the reproducer sound heads used in conjunction with commercial projectors. In these sound reproducers, an internal light source, namely, a bulb, is used to trigger or release the sound from the film as it passes over a sound drum. Heat shields and lenses are used to direct the light from this bulb toward the drum. Too much heat and the film burns; too little and the sound is garbled. Often, the bulb burns out and needs to be replaced.
Most modern movie theaters have a plurality of cinemas. Each presently uses a separate projection light source (the xenon light adjacent the projector) and another separate sound light source (the bulb inside the sound head). The initial capital investment for this multiple equipment is prohibitive, so is its upkeep.
Accordingly, a need exists for alternative light sources that can be used more safely and economically. Preferably, these light sources must be able to illuminate the film even brighter than xenon lamps, but without the present heating problems and expense of the present lamps.
It is therefore a general object of the present invention to provide a novel, cool lighting system for projecting film images from a commercial projector onto a movie screen in a theater, wherein the system overcomes the deficiencies of the prior art.
It is another general object to provide a highly concentrated, but cool, light source that prevents degradation of film previously caused by standard light sources.
It is a more specific object to provide a highly intensified, but cool, light from a fiber-optic source that can be placed closely adjacent to the film to both crisply project the film image and release the film's sound without film degradation. This low-heat light prolongs film life and reduces fire hazard.
It is another general object to provide a fiber-optic system for distributing inexpensive cool light to a plurality of projectors from a single light source. The single light source reduces the costs previously needed to run a plurality of light sources in a theater, such as their combined electricity costs and maintenance.
It is another object to provide a novel lighting system, commensurate with the above-listed objects, that can be quickly attached to or detached from a projector and a reproducer sound head. The system requires little training for theater personnel to operate it, yet is extremely safe and durable to use.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.